Prostate cancer remains one of the leading causes of cancer-related mortality in men. While localized and regional forms are generally well controlled by current treatments, metastatic disease eventually develops resistance to therapies targeting the androgen receptor, and the five-year survival rate of patients with metastatic forms is around 30%. No truly effective immunotherapy is currently available for these refractory patients. In this context, adoptive transfer of chimeric antigen receptor T cells (CAR-T) has attracted growing interest. Nevertheless, its application to solid tumors faces several obstacles: the heterogeneity and specificity of tumor antigens, potential toxicities, the migration of cells to the tumor site, the immunosuppressive nature of the microenvironment, and the hypoxia frequently associated with tumor development and correlated with poor prognosis in the prostate.
The authors explored the potential of mesothelin, a cancer-associated marker already considered promising in solid tumors, as a therapeutic target in prostate cancer. Using gene expression datasets distinguishing primary from metastatic tumors, mesothelin expression was characterized and then evaluated across various preclinical models. The efficacy of second-generation mesothelin-directed CAR-T cells (meso-CAR-T), engineered with a 4-1BB costimulatory domain, was subsequently tested under normoxia (21% O₂) and severe hypoxia (1% O₂), the latter representing a stress condition characteristic of the tumor microenvironment.
The analysis reveals a significant enrichment of mesothelin in 4 to 10% of metastatic prostate tumors, in contrast with minimal expression in primary tumors. This observation is accompanied by increased mesothelin expression in an aggressive variant of the 22Rv1 line, the 22Rv1-CR-1 model, which exhibits an epithelial-mesenchymal plasticity phenotype and stable membrane expression of the marker, including under hypoxia. An inverse correlation between mesothelin expression and androgen receptor activity was also observed. In two-dimensional co-cultures, meso-CAR-T cells demonstrated potent cytotoxicity and high selectivity toward these carcinoma cells, with minimal differences in cytolytic activity between normoxia and hypoxia. Hypoxia nevertheless induced both activation and cytotoxicity markers (GZMB, CD69, IFNG, TNFA) and exhaustion markers (LAG3, PDCD1, decreased IL2), suggesting a dual effect that warrants further investigation.
The authors acknowledge several limitations, notably the small number of available metastatic tissue samples, the reliance on public expression data, and the fact that 22Rv1-CR-1 is the only model expressing mesothelin at a notable membrane level. They emphasize that, owing to the antigenic heterogeneity of prostate tumors, targeting multiple antigens will likely be necessary. This study highlights the potential of meso-CAR-T cells as a strategy for targeting specific subtypes of metastatic prostate cancer.